Most semiconductor devices generate heat during operation. Some semiconductor devices generate a significant amount heat that is enough to adversely impact device operation. While self-heating of semiconductor devices is alleviated to some degree in semiconductor devices built on bulk semiconductor substrates due to relatively high thermal conductivity of semiconductor materials, self-heating becomes very problematic in semiconductor devices built on semiconductor-on-insulator (SOI) substrate since a buried insulator layer has poor thermal conductivity.
Thus, a typical semiconductor device built on an SOI substrate is completely surrounded by insulators such as buried insulator layer, shallow trench isolation, and a middle-of-line (MOL) dielectric layer. Metal contacts to device terminals serve as the only heat sink for the semiconductor device. Components of the semiconductor device that do not have any metal contact are thus prone to self-heating in an SOI substrate.
An example of degradation of device characteristics is shown in FIG. 1A. An ideal current response 101 of a prior art electrostatic discharge (ESD) protection diode built on an SOI substrate and having a fixed parasitic resistance under a voltage pulse for 100 ns is shown in a dotted line. The duration of the voltage pulse simulates an electrostatic discharge event. The inverse of the slope in the ideal current response is the fixed parasitic resistance of the ideal electrostatic discharge protection diode. An actual current response 102 of the electrostatic discharge protection diode under the same conditions is shown in a solid line. The actual current response 102 may be much less than the ideal current response 101, particularly under a high voltage pulse. The ESD protection diode is not capable of handling a high voltage pulse as a fixed parasitic resistance model predicts, since self-heating increases the parasitic resistance of the ESD protection diode. While the ideal current response 101 and the actual current response 102 may, in general, vary depending on dimensions of ESD protection diodes on an SOI substrate, degradation of actual current responses may be observed in the ESD protection diodes when subjected to a high voltage pulse.
FIG. 2 offers a simple model for explaining the degradation in the performance of the prior art ESD protection diode. The resistance of the parasitic resistor on the ESD diode is a temperature dependent variable. While the two end terminals of the prior art ESD protection diode is contacted by metal contacts, the body of the prior art ESD diode is not contacted by any metal. Thus, the body of the prior art ESD diode is prone to self-heating, which causes increase in the parasitic resistance.
U.S. Pat. No. 6,740,548 to Darmawan discloses a prior art semiconductor structure to alleviate self-heating of a semiconductor device formed on an SOI substrate. A portion of a buried insulator layer is removed and replaced with a conductive semiconductor material so that heat may be dissipated through a handle substrate. However, this method requires alignment of a pattern in the buried insulator layer to a heat generating semiconductor device, as well as additional processing steps such as lithographic patterning and etching of portions of the buried insulator layer.
U.S. Pat. No. 6,407,445 to Vashchenko et al. discloses another prior art structure for limiting self-heating of a semiconductor device. However, a heat sink provided by this structure may not necessarily be close to a hot spot, or the location of maximum heat generation. Further, this structure requires additional area to place a heat sink adjacent to the semiconductor device.
In view of the above, there exists a need for a semiconductor structure that may limit self-heating in a semiconductor device built on an SOI substrate by providing a heat sink in proximity to a heat generating component of the semiconductor device to effectively remove heat, while not requiring many additional processing steps or additional device areas, and methods of manufacturing the same.